1. Field of the Invention
The present invention relates to a vehicle air-conditioning system which connects, in the form of a local area network (hereinafter referred to as a LAN), an air-conditioning control unit to door actuators and controls the opening of doors through use of a target door opening, and more particularly, to a local-area-networked vehicle air-conditioning system equipped with the feature of self-diagnosing the door actuators.
2. Description of the Conventional Art
In an existing vehicle air-conditioning system equipped with a microcomputer, an intake door, an air mixing door, and a mode door are automatically controlled so as to open and close on the basis of a target opening signal calculated by the microcomputer by means of an electrically-driven actuators. At this time, in order to feed back an actual degree of opening of each door to the microcomputer, a rotational position signal is output from the electrically-driven actuator to the microcomputer. To transmit and receive such a control signal, it is necessary to electrically connect the microcomputer incorporated in an amplifier unit to the electrically-driven actuators mounted on an air-conditioning unit by means of tens of wiring harnesses. Further, the opening position required for each door becomes different for each of the intake door, the mixing door, and the mode door. Accordingly, an electrically-driven actuator whose actuation method is suitable for each door is used, thereby making it difficult to share the same actuator among doors.
For these reasons, data communication between the air-conditioning amplifier and the electrically-driven actuators is configured in a local area network to thereby reduce the number of wiring harnesses serving as transmission mediums and to integrate the electrically-driven actuators. In this type of local-area-networked vehicle air-conditioning system, the electrically-driven actuator is equipped with an IC chip which constitutes a signal processing circuit, and data are exchanged between the IC chip and the microcomputer of the amplifier unit. The feedback on the actual door opening is processed by an electronic circuit including the IC chip of the electrically-driven actuator, thereby enabling a reduction in the number of wiring harnesses. Further, this electronic circuit can control an opening position of each door, thereby enabling the electrically-driven actuator to be shared between the doors.
The existing vehicle air-conditioning system equipped with a microcomputer has a so-called self-diagnostics for checking whether or not the electrically-driven actuators are properly actuated. If any problem arises, the problem can be indicated on a monitor, or the like, by checking the operations of the electrically-driven actuators by means of the microcomputer, because the data concerning the electrically-driven actuators, such as position signals required for self-diagnostics, are all transmitted to the microcomputer as a return signal, and all the data are processed by the microcomputer.
However, in the aforementioned local-area-networked vehicle air-conditioning system, since-there is no need to feed back the position signals from the electrically-driven actuators to the microcomputer, the length of the data in the return signal transmitted to the microcomputer from the actuators has only 1 bit which represents whether the electrically-driven actuator is in operation (in a high state; Hi) or under suspension (in a low state; Lo).
As a result, even in a state where a high-level signal is being transmitted to the microcomputer, it is impossible for the microcomputer to know whether or not the electrically-driven actuator is properly operating or in a motor-locked state. Further, even in a state where a low-level signal is being transmitted to the microcomputer, it is impossible for the microcomputer to know whether the electrically-driven actuator is properly operating or stopped due to a communications error.
Further, if the return signal is simply checked in terms of the commencement of action of the door without taking into consideration the check timing corresponding to a change in an instructed degree of door opening, it will be falsely determined whether the door is actuated normally or abnormally.
More specifically, since the communication data including the return signal are sequentially sent in accordance with predetermined rotation, if there is a change in an instruction value of the data (target position of the door), the commencement of operation of the actuator will lag behind the changed instruction value. Further, the output of the return signal representing the operation of the actuator lags behind the actual commencement of operation of the actuator. Particularly, the lag time becomes longer with an increase in the number of door actuators.
These problems can be solved by only increasing the area of data in a communications frame format related to the operation of the electrically-driven actuator. However, such an increase in the data area results in a reduction in another data area related to; e.g., a target door opening signal.